1. Field of the Invention
The invention concerns a method to generate, by means of a magnetic resonance system, magnetic resonance measurement data of an examination region to be examined that is located in a measurement volume of a magnetic resonance system by radiation of preparation pulses into the examination subject and readout of k-space corresponding to the examination region as well as a magnetic resonance system electronically readable data medium with programming instructions to implement such a method being stored therein.
2. Description of the Prior Art
Magnetic resonance (MR) is a known modality with which images of the inside of an examination subject can be generated. Expressed simply for this purpose, the examination subject is positioned within a strong, static, homogeneous basic magnetic field (also called a B0 field) with field strengths of 0.2 Tesla to 7 Tesla and more, such that the nuclear spins of the examination subject orient along the basic magnetic field. To trigger nuclear magnetic resonances, radio-frequency excitation pulses (RF pulses) are radiated into the examination subject, the triggered magnetic resonance signals are measured (detected), and MR images are reconstructed or spectroscopy data are determined based on these magnetic resonance signals. For spatial coding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field. The acquired measurement data are digitized and stored as complex numerical values in a k-space matrix. An associated MR image can be reconstructed from the k-space matrix populated with such values, for example by a multidimensional Fourier transformation.
It is possible to depict soft tissue parts with high contrast by means of MR techniques. Different substances can be presented and differentiated well with suitable sequences due to their different physical properties, such as the relaxation time of the longitudinal magnetization T1, the decay time of the transverse magnetization T2, or the time constant of the free induction decay T2* (also called effective decay time of the transverse magnetization), or also precession frequencies.
The achieved image contrast can be additionally, specifically varied by the use of pulses known as preparation pulses (also known as pre-pulses). For example, such preparation pulses are preparation pulses for fat and/or water suppression or T1 or T2 preparation pulses. During the acquisition of the measurement data in the sequences, such preparation pulses are radiated into the examination subject before or in combination with the RF pulses that are used. However, a certain time duration must thereby be allotted for the preparation pulse (and possibly also for a subsequent dephasing of unwanted signals, for example—known as “spoiling”) or to relax the nuclear spins in the pulse sequence. Depending on the type of preparation pulse, the measurement time can hereby be markedly extended. In spite of this, in order to keep the measurement time short, preparation pulses are normally radiated only at every m-th excitation and acquisition of measurement data, with m typically being a number between approximately five and approximately 20. However, if m is chosen too large, it is no longer necessarily ensured that the desired contrast is achieved.